We have observed two previously unrecognized, structurally distinct collagen chains (provisionally termed alpha A and alpha B) in human tissues, and found that these new chains copurify in a 1:2 ratio. The present project seeks to determine additional structural features of these new collagen chains, such as molecular weight, glycosylation and amino acid composition of both whole chains and derived cyanogen bromide peptides. In addition, studies aimed at confirmation of the proposed structure of the native triple-helical molecule, and surveys of the tissue distribution and localization of this new collagen species will be performed. It seems likelythat this new collagen species is a component of basement membranes, and if this supposition proves true, we will extend these studies to human disorders of basement membrane, such as diabetes mellitus.